Material Aligned Process Control for the Welding Technology of Locally Hardened Materials

Abstract:

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The subproject B5 examines the welding technological processing of locally hardened
materials to produce structures and knots by means of high-freqency welding (HFW). The aim of
B5 is a defined intervention in process and plant technology to control current voltage, temperature
and compressive stress distribution of the entire weld seam. Particularly the effects on locally
hardened areas have to be measured and optimized. Also the process specific advantages of HFW
(e.g. plastic deformations and the application of an in situ heat treatment) have to be examined and
optimized to improve structural strength.

Abstract: Considering the exhaust valve spindle consists of a valve head and a stem comprising the
body, the use of different materials, that is, Nimonic 80A for the head and SNCrW for the stem, can
reduce the manufacturing cost dramatically. The inertia welding was conducted to make the large
exhaust valve for low speed marine diesel engines, superalloy Nimonic 80A for valve head of 540mm
diameter and high alloy SNCrW for valve stem of 115mm diameter. Due to different properties of
material like thermal conductivity and flow stress on the two sides of the weld interface, modeling is
crucial in determining the optimal weld geometry and parameters. FE simulation was performed by
the commercial code DEFORM-2D. A Good agreement between the predicted and actual welded
shape was observed. It was expected that simulation will significantly reduce the number of
experimental trials needed to determine the weld parameters, especially for welds of very expensive
materials or large shaft. A variety of tests, including microstructure observation, tensile, hardness and
fatigue test, are conducted to evaluate the quality of welded joints.

Abstract: This paper takes the butt joint of axle case steel as research object, simulates the real-time three dimensional dynamics CO2 shielded welding of welding stress field by FEM software ANSYS and obtains the axle case steel 390Q’s transient stress field of weld zone at different welding speed. On that basis, the feasible dynamic simulation method of three-dimensional stress welding field which provides theoretical basis and guidelines for optimizing welding technology and norm welding parameters was proposed. The result of welding stress simulation shows that the welding stress is the lowest when the optimum welding speed is 5mm/s.

Abstract: The development of high-strength structural steels with yield strengths up to 1000 MPa results in the requirement of suitable filler materials for welding. Recently designed low transformation temperature (LTT) alloys offer appropriate strength. The martensitic phase transformation during welding induces compressive residual stress in the weld zone. Therefore, the mechanical properties of welded joints can be improved. The present paper illustrates numerical simulation of the residual stresses in LTT-welds taking into account the effect of varying Ms/Mf-temperatures, and therefore different retained austenite contents, on the residual stresses. Residual stress distributions measured by synchrotron diffraction are taken as evaluation basis. A numerical model for the simulation of transformation affected welds is established and can be used for identification of appropriate Ms-temperatures considering the content of retained austenite.

Abstract: In offshore jacket platforms, the structural steels are widely used and usually welded connected. This paper presents the welding of 45# steel plate by LER-3 YAG Pulse Laser. Experiments are carried out to investigate the performance of the welded joint under different process parameters and working conditions. In details, microstructure and macro-morphology in the laser-affected area are analyzed and the micro hardness of the specimens is tested. The results show that: (a) the performance of the welded joint can be improved by the optimization of process parameters, (b) the welding area has the closest grained, the heat affected zone is isometric crystal, (c) the martensite can be reduced by increasing the heat, (d) the grain can be greatly refined by properly increasing the scan speed and decreasing the laser power supply, and that (e) the mean value of the hardness (420HV) in the welded area is obviously higher than that of the substrate (205.12HV) and the highest hardness (492.32HV) appears in the heat affected area.

Abstract: Based on artificial neural network (ANN), a mechanical properties prediction model for automatic welding is built. The input parameters of the model consist of the chemical elements and the diameter of the welding material and the outputs is the mechanical properties, i.e. yield strength, tensile strength and elongation. The ANNs model is established by Visual C++ based on improved back-propagation (BP) arithmetic with momentum coefficients, in which the sample data used are from automatic welding materials for X70 pipeline steel. The influence of chemical compositions, such as C, S, P, Si, Mn, Cu, Ti and Ni on the mechanical properties of welding materials are analyzed. The results show that the influence of metallic elements is significantly greater than the nonmetallic. For nonmetallic elements, not all the value of mechanical properties decreases with the increase of the content. The influence of C is critical, followed by P and S. For metallic elements, the influence of different elements on mechanical properties, such as the yield strength, the tensile strength, the elongation and the average Charpy impact toughness, is difference.